The invention relates to the field of electrical engineering and electronics. Objects, for which the application is possible and appropriate, are components based on acoustic surface waves, such as oscillators and sensors, especially those sensors, for which the variation in the temperature of the oscillator frequency can be adjusted.
Oscillators are known, which comprise a composite of two frequency-determining elements, of which each element contains at least one interdigital converter for acoustic surface waves and a feedback from the output to the input of the composite containing an amplifier, the frequency-determining elements differing from one another due to the temperature dependence of the synchronous frequency.
In the case of a special embodiment, the composite of two frequency-determining elements contains two delay leads, the substrates of which belong to one and the same crystalline section, but use different splitting directions (T. J. Browning and M. F. Lewis, “A novel technique for improving the temperature stability of SAW/SSBW devices” in Proc. 1978 IEEE Ultrasonics Symposium, pages 474 to 474 (1)). The ST section of quartz serves as crystalline section. In the case of the ST section, the section normal is inclined at an angle of 42.75° to the crystallographic Y axis of quartz. The substrate of the main delay lead has the X axis of quartz as the spreading direction, while the spreading direction of the auxiliary delay lead is inclined at an angle of 41° thereto. Accordingly, in the case of the main delay lead, the temperature coefficient of the synchronous frequency of the first order disappears. On the other hand, the temperature coefficient of the synchronous frequency of the first order of the auxiliary delay lead is not equal to zero. In spite of the different orders of the temperature coefficients, it is possible to compensate for the temperature coefficient of the synchronous frequency of second order of the main delay lead. The temperature coefficient of the synchronous frequency of first order of the auxiliary delay lead, required for compensating for the temperature coefficient of the synchronous frequency of second order of the main delay lead, is given as a function of the temperature coefficient of second order, which is to be compensated, of the amplitude of the auxiliary delay lead and of the spreading segment, which is the same for the two delay leads.
In connection with sensors, which can be polled remotely and contain, in the special case, single gate resonators based on acoustic surface waves, it is known that, for temperature, compensation, two single gate resonators may be combined, the substrates of which represent different splitting directions of one and the same crystalline section (A differential measurement SAW device for passive remove sensoring, W. Buff, M. Rusko, T. Vandahl, M. Goroll and F. Möller, Proc. 1996 IEEE Ultrasonics Symposium, pages 343 to 346 (2)). In this connection, it is a prerequisite for the temperature compensation that the spreading directions have different phase velocities and almost the same temperature coefficients of the synchronous frequency.
The solution, described in the publication (1), has the following disadvantages:                1) The phase slope of the delay leads of specified substrate length may be too small, so that the oscillators are insufficiently stable.        2) The size |S21| at the oscillator frequency, which sets in as a function of temperature, depends too much on the temperature, so that the amplifier in the feedback, as a result of an excessively large amplification range, causes undesirable, nonlinear effects or, as a controlled amplifier, excessively high costs.        3) The method of temperature compensation from (1) can be used only for broadband frequency-determining elements.        4) The model for describing the composite of two delay leads, used in (1), is an approximation for the case that the input and output impedance of the composite of the delay leads is very large in comparison to the source or load resistance and all converters are reflection-free. The teachings, obtained with the help of this model, for example, the above-mentioned function for the temperature coefficient of the synchronous frequency of first order of the auxiliary delay lead, is therefore in many cases not applicable and cannot be transferred to those frequency-determining elements, for which reflections play an important role.        